How climate change contributed to Colorado flood

It has become a familiar pattern. A natural disaster occurs and we can't help but wonder how it may have been influenced by climate change. With more than 97% of 11,944 peer-reviewed papers by climate scientists agreeing that global warming is man-made and basic physics and climate models predicting that a warmer atmosphere will lead to heavier rains, it's understandable that the incredible rains that fell on Colorado would lead us to wonder what role climate change played in the devastating floods.

Atmospheric water vapor fed by the remnants of two tropical storms—one in the Gulf of Mexico and another in the Pacific Ocean—had already reached the highest level ever measured in Colorado for September, usually one of our driest months. At the same time, a stationary high-pressure system to the east and a deep low to the west had trapped all that moisture up against the Rocky Mountains. Powerful easterly winds forced the moisture upward, where it quickly condensed in the cooler air, resulting in last week’s deluge.

In Colorado, these “upslope” storms are typically small and don’t last long—because the conditions to generate them rarely align for more than 12 hours. But not this time. Instead, optimal conditions persisted for nearly a week across a vast area from central Colorado to the Wyoming border. That’s why some meteorologists have called “Superflood 2013” a millennial storm: in any given year, they say, there’s only a one-in-1,000 chance that the atmospheric variables would come together to produce a tempest of such magnitude.

In addition to the increased moisture in the atmosphere, other side effects of global warming exacerbated the damage done by the floods. Amy Goodman and Nermeen Shaikh at Democracy Now! spoke with Bill McKibben and Jim Pullen, a reporter from KGNU in Boulder, Colorado about the role the pine beetle infestation and wildfires had on the flooding:

AMY GOODMAN: And that issue of climate change, can you talk about, for example, also the pine beetle, how it has devastated millions of acres, making them weaker? Then you have the forest fires, then less ability to maintain water in the soil with the trees not there and then you have flooding like this that intensifies the devastation.

JIM PULLEN: I think of this is as sort of a perfect storm in the sense that the underlying ecosystem has been damaged by fires. Now, fires are localized compared to this storm, on the order of 20 or 30 or 40 square miles may be affected by a fire. This storm has spread over hundreds of square miles. But, locally, and in the watersheds where the terrain is steep, the ecosystem has been severely damaged.

When you drive in the mountains of our state, there are vast patches of dead trees. Scientists still debate whether or not these dead trees might lead to more or fewer fires, but the common wisdom is that they would certainly lead to more fires because they are dead trees. So I feel like those have played a part. Now this storm was so intense and so massive and persisted for so long that we would have still seen incredible destruction even without the fire damage, even without the pine beetle damage.

Making the situation even worse is the damage done to the many oil and gas wells that were flooded. Jim Pullen explains:

Of course, in any flood event, there are going to be a lot of contaminants in the water. There are going to be dead animals, there are going to be — there are oil stations — gasoline stations that have been inundated. People’s homes have been inundated, and people keep a lot of chemicals in their homes that are under relatively low protection.

We have some very serious issues here in the state of Colorado in addition to those normal flooding issues. We have the Rocky Flats plant, or what was once upon a time the Rocky Flats Plant where plutonium is underground. And there has been extensive flooding in that area. And we also have tens of thousands of active oil and gas wells in the state, 20,000 alone in Weld County. The industry — a lobbying group is reporting 1900 of those oil and gas wells have been shut down, and including the two largest suppliers, Noble Energy and Anadarko are reporting about five to ten percent of their wells have been shut down.

For example, Noble Energy owns 7600 wells in Weld County itself, which is right to the northeast of us. So, there are a lot of contaminants potentially floating around. And in the case of Rocky Flats, I spoke with a Christine Everson last night and she said it is going to take weeks for laboratory results of plutonium and other contaminants to become available to the public.

At Mother Jones, Chris Mooney explains why climate scientists are usually hesitant to say any particular weather event was caused by climate change:

The issue is further complicated by a large gap between how scientists understand the word “cause,” and how the lay public does.

Ordinarily, we think about “cause” in a simple sense in which one thing fully brings about another. Thus, I tripped and fell, and this caused me to have a bump on my head. But in the atmosphere, it’s hardly so simple. As we’ve seen, the Colorado floods were partially caused by moisture from the tropics, partly caused by a blocking pattern that held one weather system in place for an extended period of time, and perhaps also partly caused by past wildfires that increased the risk of runoff (to name just a few partial causes). The cognitive linguist George Lakoff has introduced the distinction between “direct causation” and “systemic causation” to help us tackle this sort of problem. The latter form of causation is not direct; rather, it is diffuse, partial, and usually captured in statistical relationships. But it is no less real for this reason, or less amenable to scientific analysis.

With every extreme weather event nowadays, from Superstorm Sandy to the Colorado floods, there’s a strong inclination to link it to climate change. But once you get into the details, the word “link” becomes far too vague: Each event is different, and the ways in which it may or may not relate to a changing climate are also varied. Partial contributions may be present—global warming exacerbated Sandy’s storm surge through sea level rise, and probably contributed to some percentage of the rainfall over Colorado—and individual events may be consistent with larger trends. But ultimate “causal” connections remain difficult to establish and, according to Trenberth, the very attempt itself may be missing the point.

Mooney's Bottom line:

"And the proper way of thinking about that situation is clear: Even when you can’t be definitive, you can definitely be worried."